Vacuum Induction Melting (VIM) is a method used to melt new alloys or recycled materials in a vacuum or inert atmosphere. This prevents oxidation and contamination from the atmosphere. It is commonly used to produce high-temperature alloys, precision alloys, and other special alloys. The first vacuum induction furnace was built in 1917 by the German company Heraeus to melt nickel-chromium alloys used in aircraft and rocket engines. Today, vacuum induction furnaces are crucial equipment for implementing the VIM process and are key to producing various special materials. The furnace’s design is vital for achieving and ensuring the quality of the VIM process. There are four main structures of Vacuum induction melting furnace with types including batch, vertical, horizontal, and VIDP. This article will analyze the main structural types of vacuum induction furnaces.
1. Structural Types of Vacuum Induction Melting Furnace
Over more than 100 years of development, vacuum induction melting furnaces have evolved into several types. Although all these furnaces serve the VIM process, they differ significantly in structure due to their specific purposes and design concepts. Broadly, vacuum induction melting furnaces can be divided into batch and continuous types. The continuous type is more diverse, with variations such as vertical continuous, horizontal continuous, and VIDP models. Below are the main structural types.
1.1 Batch Type
The batch-type vacuum induction melting furnace is the simplest and the earliest design. It is technologically mature. The furnace structure is relatively simple, with the melting chamber (furnace body) as the main vacuum chamber. Inside the melting chamber, there are the melting coil and coil rotation mechanism, and the furnace is connected to vacuum, temperature measurement, and feeding systems. Batch-type furnaces are easy to operate and cost-effective. However, since the melting chamber must be exposed to air after each melting cycle, the production efficiency is low. These furnaces are mainly used for laboratory work and small batch testing, not as mainstream industrial production equipment.
1.2 Vertical Continuous Type
The vertical continuous vacuum induction melting furnace is an important branch of continuous-type furnaces. It is typically used for capacities ranging from 100 to 500 kg. The furnace generally adopts a vertical three-chamber structure, consisting of a temperature/feeding chamber (usually a feeding and temperature measurement turret), a melting chamber, and a casting chamber. Each chamber is separated by isolation valves. The mold (casting) is repeatedly moved in and out of the casting chamber. Secondary feeding and temperature measurements are done through the feeding/temperature chamber. The melting chamber always remains in a vacuum, enabling continuous vacuum induction melting.
The melting coil in a vertical continuous furnace usually adopts a non-magnetic yoke structure. This is because, for smaller furnaces, a non-magnetic coil offers a better cost-performance ratio. If a magnetic yoke structure is used, it would increase the furnace size, making the entire furnace (melting and casting chambers) top-heavy, which is unsuitable for a vertical structure.
The vertical continuous furnace dates back to a patent by Consolidated Electrodynamics Corporation in the 1950s. Later, Germany’s Leybold-Heraeus Company significantly promoted its development. Over time, this furnace type has gone through several technological iterations. It has not only excelled in the melting furnace field but also influenced the development of other furnaces, such as precision casting furnaces.
1.3 Horizontal Continuous Type
The horizontal continuous vacuum induction melting furnace typically has a capacity ranging from 1 to 30 tons, with some models reaching 60 tons. This structure is better suited for larger furnaces, meeting the requirements for larger capacities, usability, and structural stability. Horizontal continuous furnaces can be flexibly designed based on capacity, function, and mold size.
1.4 VIDP Type
The VIDP vacuum induction melting furnace was proposed by Germany’s Leybold-Heraeus Company in the 1980s and patented. It is essentially a variant of the horizontal continuous VIM furnace. VIDP stands for Vacuum Induction Degassing and Pouring. The main feature of this furnace is that it integrates the melting chamber and the melting tilting device. During pouring, both the furnace body and the coil tilt together. This design greatly reduces the size of the melting chamber. For example, a 5-ton VIDP furnace has a melting chamber volume of about 11 m³, while a traditional VIM furnace would be around 60 m³. Therefore, the VIDP furnace requires much less time to evacuate the melting chamber compared to a traditional VIM furnace.
Another significant advantage of the VIDP furnace is its degassing and slag filtration function. This is achieved through a dedicated long-flow (steel) channel. The long-flow channel connects the melting and casting chambers, allowing the steel to degas during its transfer. Multiple slag barriers can be placed in the channel to filter out impurities.
In addition to these benefits, the VIDP furnace has external water-cooled cables to prevent the cables from being burned by molten steel. It also lacks hydraulic components inside the furnace, offering other advantages.
Conclusion of Structures of Vacuum Induction Melting Furnace
Vacuum induction melting furnaces have evolved significantly to meet the demands of modern alloy production. Each furnace type has unique advantages that suit different applications, from laboratory-scale operations to large-scale industrial production. Whether it’s the simplicity and cost-effectiveness of the batch-type furnace, the continuous operation of the vertical or horizontal continuous furnaces, or the innovative features of the VIDP furnace, these technologies have become indispensable in industries requiring high-purity and high-performance materials. The continuous advancement in furnace design and functionality demonstrates the crucial role that vacuum induction melting plays in modern metallurgy and materials science.
